Wall display devices, such as electric bulletin boards and advertisement sign boards, are widely used as means for providing information to many and unspecific people on streets. Such a wall display device usually includes a number of display elements arranged on a plane in which an individual element is used for one pixel. The respective display elements are electrically actuated in various manner to display information. In an electric bulletin board, for example, one light bulb is used as one display element for one pixel, and a plurality of the light bulbs are arranged in matrix. By illuminating those of the light bulbs in specified positions, it is possible to display letters and pictures. Recently electric bulletin boards using light emitting diodes in place of the light bulbs are widely used.
An advertisement sign board uses "panel display elements" as display elements constituting respective pixels. The "panel display elements" are not light emitting themselves but have a plurality of display faces only one of which is actually displayed. Usually one of the display faces to be displayed can be selected by using a rotary mechanism, such as a motor or the like. One display face is selected for each pixel, whereby letters or pictures can be displayed.
The display elements for respective pixels, which are thus provided by light bulbs, light emitting diodes, panel display elements or the like, are electrically actuated. The light bulbs and the light emitting diodes, for example, can be switched between their light emitting state and non-light emitting state by On/Off control of electric power supply. By conducting the On/Off control on the respective light bulbs or the respective light emitting diodes providing the respective pixels, only required pixels can be selectively illuminated, whereby required information can be displayed. In the panel display elements the On/Off control of electric power supply to the motor is conducted, whereby those of the display faces to be actually displayed can be selected. The On/Off control is conducted on the respective panel display elements providing the respective pixels, whereby a required display face for each pixel can be displayed and required information can be displayed.
In the above-described display devices, needless to say, larger numbers of pixels are necessary for improvement of their display resolution. Accordingly it is necessary that a large number of display elements for respective pixels are arranged in a matrix. As described above, since display manners of the respective display elements must be controlled by electric power supply, it is needed to provide an individual electric power supply line for the individual display elements. In an electric bulletin board having 100 light bulbs arranged in a matrix, for example, two electric power supply lines are needed for each of the 100 light bulbs, and therefore totally 200 lines must be wired from a switchboard to the light bulbs. For high resolution a lager number of light bulbs must be arranged, which increases a number of wiring lines. When a number of wiring lines becomes increased, a structure of a display device becomes complicated, which need much labor for its manufacture and maintenance. This results in higher manufacturing costs and maintenance costs.
An object of the present invention is to provide a display device which can simplify wiring for respective display elements, and facilitates manufacturing and maintenance of the device.